1. Technical Field
The present invention relates to control method for a fluid ejection device having a fluid ejection head with a plurality of nozzles for discharging a fluid, and to the fluid ejection device.
2. Related Art
Inkjet printers have a printhead with a plurality of nozzles that discharge ink droplets, and the printhead is mounted on a carriage with the nozzle surface where the plural nozzles are arranged facing down. Inkjet printers that have a head maintenance mechanism for maintaining the printhead exposed below the carriage are also known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2009-190282.
The head maintenance mechanism of the inkjet printer taught in JP-A-2009-190282 includes a wiper mechanism that physically wipes the nozzle surface, and an ink suction mechanism that suctions ink from the nozzles. The head maintenance mechanism also functions as an ink droplet ejection test device that checks if ink droplets are ejected from the plural nozzles normally (that is, checks to find any clogged nozzles). The head maintenance mechanism checks whether or not ink droplets are ejected from the plural nozzles based on a current change that occurs when charged ink discharged from the nozzles lands on a sponge (absorbent material) disposed inside the head maintenance mechanism.
The inkjet printer taught in JP-A-2009-190282 runs the ink droplet ejection test of the ink droplet ejection test device every time after a predetermined number of pages have been printed. If dropped dots resulting from a nozzle not discharging ink are confirmed by the ink droplet ejection test, an operation to eliminate the dropped dots is performed. Operations to eliminate dropped dots may include, for example, a cleaning operation that suctions ink from the nozzles by means of the ink suction mechanism, and a wiping operation that wipes the nozzle surface by means of the wiper mechanism. Because the cleaning operation suctions ink from the nozzle surface, dropped dots can be reliably eliminated by running the cleaning operation when dropped dots are confirmed, but this increases ink consumption. On the other hand, because the wiping operation does not suction ink, dropped dots can be eliminated while reducing ink consumption if the wiping operation is performed when dropped dots are confirmed.
However, our studies have confirmed that the following problem can result when dropped dots are eliminated using the wiping operation. More specifically, our tests showed that ink can be forced into a nozzle by the wiping operation without the wiping operation actually eliminating the dropped dots, and this ink can then discharged from the nozzle in the ink droplet ejection test. As a result, the ink droplet ejection test falsely indicates that the dropped dots were eliminated even though they were not actually eliminated. When printing then proceeds, dropped dots reappear in the printed output because the faulty nozzles were not actually restored and the dropped dots were not actually eliminated.